The reduction and elimination of matrix interferences in graphite furnace atomic absorption spectrometry

The approaches to reduction or elimination of matrix interferences encountered in graphite furnance atomic absorption spectrometry is reviewed. These techniques include matrix modification, application of active gas, and coating tubes with metallic compounds. The research work carried out in the author's laboratory is emphasized. A more universal matrix modifier, palladium, is proposed for the determination of mercury, lead, tellurium, bismuth, arsenic, thallium and indium in environmental samples.     

Optimization of a chemical modifier in the determination of selenium by graphite furnace atomic absorption spectrometry and its application to wheat and wheat flour analysis.

A method for the determination of total selenium in wheat and wheat flour using graphite furnace atomic absorption spectrometry (GFAAS) with palladium/ascorbic acid as a chemical modifier was studied. The effects of nickel nitrate, palladium/ascorbic acid, and palladium/magnesium nitrate as chemical modifiers on the sensitivity in the determination of selenite, selenate and selenomethionine by GFAAS were compared. The palladium/ascorbic acid modifier was used for the determination of total selenium in wheat and wheat flour, because the oxidation states of the selenium ion are not important in the determination. The detection limit was estimated to be 1 microg L(-1) (calculated as 3sigma of the blank); the calibration curve was linear for the concentration range 5 - 50 microg L(-1) and the recovery range was 96.66 - 101.80%. The optimal ashing and atomizing temperatures were 1300 degrees C and 2250 degrees C, respectively. The proposed method was successfully applied to the determination of total selenium in wheat and wheat flour.     

Analyses without calibration curve for determination of indium in sediment and geochemical samples

Influences of atomization temperatures on the characteristic mass and the atomic absorption coefficient of indium were studied. The results show that the values of characteristic mass obtained from the wall, using the platform and the V-shaped boat have appeared to be stable to better than 10, 6 and 12% in the range of 1600–2400 °C, respectively. The determination of indium without calibration curve by furnace with the V-shaped boat using palladium and ammonium salt of EDTA as a matrix modifier are described. The proposed method was applied to the determination of indium in standard sediment and geochemical reference samples and satisfactory results were obtained.     

Evaluation of electrodeposited tungsten chemical modifier for direct determination of chromium in urine by ETAAS

The direct determination of chromium in urine by electrothermal atomic absorption spectrometry (ETAAS) using graphite tubes modified with tungsten is proposed. Modification of the graphite is made by tungsten electrodeposition over the whole surface atomizer followed by carbide formation by heating the tube inside its own furnace. For tungsten electrocoating, the graphite tube and a platinum electrode were connected to a power supply as cathode and anode, respectively, and immersed in a solution containing 2 mg of W in 0.1% v/v HNO₃. Then, 5 V was applied between the electrodes during 20 min for tungsten electrodeposition over the whole atomizer. A SpectrAA 220 Varian atomic absorption spectrometer equipped with a deuterium background corrector was used throughout. Undiluted urine (20 μl) was delivered over the tungsten-treated tube and the chromium-integrated absorbance was measured after applying a suitable heating program with maximum pyrolysis at 1300 °C and atomization at 2500 °C. With electrodeposited tungsten modifier, the tube lifetime increased up to four times when compared to previous published methods for Cr determination in urine by ETAAS, reaching 800 firings. Method detection limit (3 S.D.) was 0.10 μg l⁻¹, based on 10 integrated absorbance measurements of a urine sample with low Cr concentration. Two reference materials of urines (SRM 2670) from National Institute of Standards and Technology (NIST) were analyzed for method validation. For additional validation, results obtained from eight human urine samples were also analyzed in a spectrometer with Zeeman effect background correction.     

微波消解–石墨炉原子吸收光谱法测定空气中碲

建立微波消解–石墨炉原子吸收光谱法测定空气中的碲。采用微孔滤膜收集样品,以硝酸–双氧水混合体系微波消解滤膜,氯化钯为基体改进剂,在优化的仪器工作条件下测定。碲的质量浓度在0~15μg/L范围内与吸光度线性关系良好,相关系数为0.999 5,方法检出限为0.14μg/L。样品加标回收率在95.6%~104.0%之间,测定结果的相对标准偏差为1.15~1.37%(n=7)。该方法操作简单、灵敏度高,适用于空气中微量碲的测定。     

Direct Determination of Arsenic in Beet Sugar Molasses Using Nickel as Chemical Modifier by Electrothermal Atomic Absorption Spectrommetry

A simple electrothermal atomic absorption spectrometric (ETAAS) method is described for direct determination of arsenic in sugar beet molasses samples. Pyrolytic graphite tubes were used as atomizers. The compression between modifiers such as nickel nitrate, palladium nitrate and the mixture of palladium and magnesium nitrate were performed and nickel nitrate selected as the best chemical modifier. The effects of pyrolysis and atomization temperature were also studied and the pyrolysis temperature of 900 °C and atomization temperature of 2300 °C have been chosen for temperature program. The detection limit of the method was 1 ng/mL As in sugar beet molasses samples. The relative standard deviation for ten determination of a spiked sample with concentration of 50 ng/mL As was 2.4%. The accuracy of the method was confirmed by the analysis of spiked samples. The linear rang of calibration is in the range of 1‐100 ng/mL of arsenic.     

Noble metals as permanent chemical modifiers for the determination of mercury in environmental reference materials using solid sampling graphite furnace atomic absorption spectrometry and calibration against aqueous standards

Iridium, palladium, rhodium and ruthenium, thermally deposited on the platform, were investigated as permanent modifiers for the determination of mercury in ash, sludge, marine and river sediment reference materials, ground to a particle size of 50 μm, using solid sampling graphite furnace atomic absorption spectrometry. A total mass of 250 μg of each modifier was applied using 25 injections of 20 μl of modifier solution (500 mg l⁻¹), and executing a temperature program for modifier conditioning after each injection. The performance of palladium was found to be most consistent, taking the characteristic mass as the major criterion, resulting in an excellent correlation between the measured integrated absorbance values and the certified mercury contents. Mercury was found to be lost in part from aqueous solutions during the drying stage in the presence of all the investigated permanent modifiers, as well as in the presence of the palladium and magnesium nitrates modifier added in solution. A loss-free determination of mercury in aqueous solutions could be reached only after the addition of potassium permanganate, which finally made possible the use of aqueous standards for the direct analysis of solid samples. A characteristic mass of 55–60 pg Hg was obtained for the solid samples, using Pd as a permanent modifier, and also in aqueous solutions after the addition of permanganate. The results obtained for mercury in ash, sludge and sediment reference materials, using direct solid sapling and calibration against aqueous standards, as well as the detection limit of 0.2 mg kg⁻¹ were satisfactory for a routine procedure.     

Determination of indium in minerals,river sediments and coal fly ash by electrothermal atomic absorption spectrometry with palladium as a matrix modifier

A method is described for the determination of indium (10–40 μg g^?1) in lead-zinc ores and magnetic pyrites. Graphite furnace atomic absorption spectrometry is used with palladium as a matrix modifier. Indium (down to 0.085 μg g^?1) in river sediments and coal fly ash can be determined after pre-extraction with ammonium iodide into 4-methyl-2-pentanone. In the presence of palladium, the maximum tolerable ashing temperatures for indium in aqueous solution or organic extract can be raised to 1200°C or 1000°C, respectively, and the sensitivity is greatly improved.     

Determination of indium by graphite furnace atomic absorption spectrometry after coprecipitation with chitosan.

A sensitive and simple method for the determination of trace amounts of indium in water samples by graphite furnace atomic absorption spectrometry (GFAAS) after coprecipitation with chitosan was investigated. Indium was quantitatively preconcentrated from water samples by coprecipitation with chitosan at pH 7.0-9.0. The coprecipitant was easily dissolved with acetic acid, and indium in the resulting solution was determined by GFAAS. The addition of lanthanum as a chemical modifier was more effective for the atomic absorbance of indium. The detection limit (S/N > or = 3) for indium was 0.04 microg dm(-3), and the relative standard deviations (n = 5) were 3.5-4.5% at 1.0 microg/100 cm3. The results obtained in this study indicate that the proposed method can be successfully applied to the determination of trace indium in water samples.     

Kinetics of indium atomization from different atomizer surfaces in electrothermal atomic absorption spectrometry (ETAAS)

The kinetic parameters of indium atomization in electrothermal atomic absorption spectrometry (ETAAS) have been determined by a newly proposed method. Effect of the atomizer surface and the palladium modifier on the kinetics of indium atomization has been investigated. The mechanisms of indium atomization seem to be identical for the pyrolytically coated graphite and the uncoated graphite tubes, i.e. the rate-limiting step for the atomization changes from a first order kinetics at lower temperatures into a nearly 1/3 order kinetics at higher temperatures, which may suggest that the analyte moves from a dispersed state to agglomates with increasing temperature. However, for the zirconium coated graphite tube, the atomization of indium is controlled by a single mechanism with the kinetic order of near 2/3 and the activation energy of 186 ± 13 kJ/mol. Relatively weak indium—zirconium carbide interactions and the release of indium from the sphere of molten indium metal on the zirconium coated surface are suggested. In the presence of palladium, a simple mechanism, i.e. the release of indium from the solid solution of the In and the Pd on the pyrolytically coated graphite surface, is proposed to account for the observed first order kinetics and the activation energy of 421 ± 27 kJ/mol.     

Prochlorperazine bismethanesulfonate as a new reagent for the spectrophotometric determination of palladium

A simple, rapid, and selective method for the determination of palladium is described. The orange-red palladium(II)-prochlorperazine bismethanesulfonate complex in the presence of hydrochloric acid-sodium acetate buffer exhibits maximum absorbance at 480 nm with a molar absorptivity of 4.32 × 10³ liters mol^?1 cm^?1. The sensitivity of the reaction is 24.62 ng cm^?2. The system obeys Beer's law over the concentration range 0.4–20 ppm of palladium with an optimum concentration range of 1–19 ppm. The apparent stability constant of the complex is found to be log K = 5.3 ± 0.1 at 27 °C. The effects of pH, time, temperature, order of addition of reactants, reagent concentration, and interferences from various ions are reported. The proposed method offers the opportunity to carry out the determination at room temperature without the need for an extraction step. The method is also found to be suitable for the determination of palladium in jewelry alloy.     

Simultaneous determination of manganese and selenium in serum by electrothermal atomic absorption spectrometry

A method for determination of manganese and selenium in serum by simultaneous atomic absorption spectrometry (SIMAAS) is proposed. The samples (30 mul) were diluted (1+3) to 1.0% v/v HNO(3)+0.10% w/v Triton X-100 directly in the autosampler cups. A total of 20 mug Pd+10 mug Mg(NO(3))(2) was used as chemical modifier. The pyrolysis and atomization temperatures for the simultaneous heating program were 1200 and 2300 degrees C, respectively. The addition of an oxidant mixture (15% w/w H(2)O(2)+1.0% v/v HNO(3)) and the inclusion of a low temperature pyrolysis step (400 degrees C) attenuated the build-up of carbonaceous residues onto the integrated platform. An aliquot of 15 mul of the reference or sample solution was introduced into the graphite tube and heated at 80 degrees C; subsequently, 10 mul of oxidant mixture+10 mul of chemical modifier was introduced over that aliquot and the remaining heating program steps were executed. This strategy allowed at least 250 heating cycles for each THGA tube without analytical signal deterioration. The characteristic masses for manganese (6 pg) and selenium (46 pg) were estimated from the analytical curves. The detection limits were 6.5 pg (n=20, 3delta) for manganese and 50 pg (n=20, 3delta) for selenium. The reliability of the entire procedure was checked with the analysis of serum from Seronormtrade mark Trace Elements in Serum (Sero AS) and by addition and recovery tests (97+/-9% for manganese and 96+/-7% for selenium) using five serum samples.     

Nickel and strontium nitrates as modifiers for the determination of selenium in wine by Zeeman electrothermal atomic absorption spectrometry

A mixed matrix modifier of nickel and strontium nitrates was used as a chemical modifier for the determination of selenium in wines by Zeeman electrothermal atomic absorption spectrometry. Wine samples were heated on a boiling water bath with small amounts of nitric acid and hydrogen peroxide. For complete elimination of interference, especially from sulfates and phosphates, selenium is complexed with ammonium pyrolidinedithiocarbamate (APDTC), extracted into methyl isobutyl ketone (MIBK), and measured by ETAAS. The graphite furnace temperature program was optimized for both aqueous and organic solutions. Pyrolysis temperatures of 1300 degrees C and 800 degrees C were chosen for aqueous and organic solutions, respectively; 2700 degrees C and 2100 degrees C were used as optimum atomization temperatures for aqueous and organic solutions, respectively. The optimum modifier mass established is markedly lower than those presented in the literature. The platform atomization ensures pretreatment stabilization up to 1100 degrees C and 1600 degrees C, respectively, for organic and aqueous selenium solutions. The procedure was verified by the method of standard addition. The investigated wine samples originated from the different regions of the Republic of Macedonia. The selenium concentration varied from not detectable to 0.93 microg L(-1).     

石墨探针—原子吸收光谱法测定人发中痕量铟的研究

探针原子化技术是一种实现等温原子化,改善灵敏度的行之有效的方法。本文采用此方法对痕量钿进行了一系列条件试验,峰面积与钿浓度在0～50ng·ml~(-1)范围内呈线性关系,其特征量4.8pg,检出限21.5pg,相对标准偏差5.7％,并成功地测定了成人发中铟的含量,范围在12～159pg·g~(-1),回收率96.4％～103.2％。该方法灵敏度高,操作简单、快速,结果满意。     

Feasibility of eliminating interferences in graphite furnace atomic absorption spectrometry using analyte transfer to the permanently modified graphite tube surface

A procedure is proposed to avoid spectral and/or non-spectral interferences in graphite furnace atomic absorption spectrometry (GF AAS) by transferring the analyte during the pyrolysis stage from a solid sampling platform to the graphite tube wall that has been coated with a permanent modifier, e.g. by electrodeposition of a platinum-group metal. The direct determination of mercury in solid coal samples was chosen as a model to investigate the feasibility of this idea. The graphite tube surface was coated with palladium and the analyte was transferred from the solid sampling platform to the tube wall at a temperature of 500±50 °C. A characteristic mass of m₀=64 pg Hg was obtained for an atomization temperature of 1300 °C, proposing a quantitative transfer of the analyte to the tube wall. Calibration against aqueous mercury standards was not feasible as this element was lost in part already during the drying stage and could not be trapped quantitatively on the modified graphite tube surface. However, the results for all except one of the coal reference materials were within the 95% confidence interval of the certificate when the slope of a correlation curve between the integrated absorbance, normalized for 1 mg of sample, and the certified value for mercury was used for calibration. A detection limit of 0.025–0.05 μg g⁻¹ Hg in coal, calculated from three times the standard deviation of the investigated coal samples, could be obtained with the proposed method. The spectral interference due to excessive background absorption in the direct determination of mercury in coal could be eliminated completely. It is expected that this analyte transfer can be used in a similar way to eliminate other spectral and/or non-spectral interferences in the GF AAS determination of other volatile analytes.     

Determination of arsenic, cadmium, lead and selenium in highly mineralized waters by graphite-furnace atomic-absorption spectrometry

A graphite-furnace AAS method using the stabilized-temperature platform furnace (STPF) concept, mixed palladium and magnesium nitrates as chemical modifier and Zeeman background correction has been applied to the direct determination of As, Cd, Pb and Se in highly mineralized waters used for medicinal purposes. These contain 20-40 g/l. concentrations of salts, mainly sodium and magnesium chlorides, bicarbonates and sulphates. The use of a pre-atomization cool-down step to 20 degrees in the graphite-furnace programme reduced the background absorption. Increasing the mass of magnesium nitrate modifier to 5 times that originally proposed improved the analyte peak shape. Under these conditions, no interference was found in analysis of the chloride/bicarbonate type of water, but the sodium and magnesium sulphate type of water had to be diluted, and even then an interference remained. Calibration with matrix-free standard solutions was used, but use of spike recovery is strongly recommended for testing the accuracy. The limits of determination (4.65sigma) of the proposed method for undiluted samples are 2.0 mug/l. for As, 0.05 mug/l. for Cd, 1.0 mug/l. for Pb and 1.5 mug/l. for Se.     

Direct electrothermal atomic absorption spectrometry determination of nickel in sea water using multiple hot injection and Zeeman correction

Methods for the direct determination of Ni in sea water samples by ETAAS were developed using Zeeman effect background correction system (ZEBC) and a multi-injection technique. A mass of palladium nitrate of 2.5 mug (for an injection volume of 100 mul) was used as chemical modifier. The optimum pyrolysis and atomization temperatures were 1700 and 2100 degrees C, respectively. The characteristic mass (m(0)) and characteristic concentration (C(0)), precision and accuracy were studied for different injection volumes (20, 100 and 200 mul). For an injection volume of 100 mul (five 20 mul aliquot) of sample the accuracy analysis of different certified materials (saline and non saline water) was agreeable. The total time of the proposed procedure is 6 min. A m(0) and C(0) of 34.5 pg and 0.3 mug l(-1), respectively were obtained for this injection volume (100 mul). Finally, interferences from major and minor components of sea water was studied.     

Kinetics of selenium atomization in electrothermal atomization atomic absorption spectrometry (ETA-AAS). Part 2: selenium with palladium modifiers

The kinetics of the atomization process of selenium with prereduced and unreduced palladium nitrate modifiers were investigated. It was found that stabilization, in both forms, occurred by principally physical processes, as opposed to compound formation. For the unreduced modifier, it was shown that higher pyrolysis temperatures resulted in a higher activation energy of atomization and that the selenium vapour-surface interaction was increased. The importance of the second high temperature step in the stabilization mechanism was stressed, and an additional conditioning step in the furnace program was proposed for the unreduced palladium modifier. The reaction order for the unreduced modifier was near first order (1.29) with an activation energy of 330 kJ mol⁻¹ and a frequency factor in the order of 1 × 10⁹. For the reduced palladium modifier, a reduction temperature of 500°C–700°C was shown to be most effective. The reduced palladium modifier showed second order kinetics and the activation energy of 500 kJ mol⁻¹, was nearly 50% higher than that of the unreduced form. This and the large frequency factor (ca. 1 × 10¹⁵) indicated strong surface interactions, thus providing an explanation to the better stabilization properties observed for the reduced form of the modifier.     

Development of a new method for direct determination of selenium associated with atmospheric particulate matter using chemical modifiers and graphite probe furnace atomic absorption spectrometry

Direct determination of selenium on or in atmospheric particulate matter (APM) has been achieved using an integrated filtration and analysis system developed in our laboratories. The filtration (sampling) and analysis system consists of a porous electrographite plate which is used initially for the purpose of collecting APM and subsequently as a probe in graphite probe furnace atomic absorption spectrometry. Selenium produced a double peak when it was atomized from such an electrographite probe. Palladium nitrate+magnesium nitrate, as a mixed chemical modifier or ascorbic acid as a chemical modifier, eliminated the double peak. The addition of the chemical modifier(s) also removed the unpredictable changes in the peak-height and the peak-area absorbance which occurred from one atomization cycle to the next if the chemical modifier was not used. Precision of 5% RSD (peak-area absorbance) was obtained for an aqueous solution of selenium standard containing 1.25 ng of selenium with palladium nitrate+magnesium nitrate mixed chemical modifier, or ascorbic acid chemical modifer. The characteristic masses and the limits of detection for the aqueous solution of selenium standard with palladium nitrate+magnesium nitrate mixed chemical modifier are 27 and 41 pg (peak-area absorbance), respectively, and with ascorbic acid chemial modifier are 29 and 36 pg, respectively (peak-area absorbance). The results of analysis of the NIST (formerly National Bureau of Standards) Standard Reference Material No. 1648, Urban Particulate Matter, for selenium with palladium nitrate+magnesium nitrate mixed chemical modifier gave a recovery of 92%, and a precision of 10% RSD, and characteristic mass and the limit of detection of 20 and 37 pg, respectively.     

石墨炉原子吸收光谱法测定碘化铯晶体中铊

采用平台石墨炉原子吸收光谱法测定了碘化铯晶体中铊。研究了碘化铯对钯－硝酸镁基本改进剂中铊吸光度影响,用预混合钯－硝酸镁和样品溶液,由于在碘化物溶液中易析出金属钯而使测定结果降低。用样品溶液和基体改进剂分别加入到石墨炉中的标准加入法可得到满意的结果。